Fire-fighter training

ABSTRACT

A fire simulator comprises fuel distribution means ( 12 ) under a grating ( 6 ) through which fuel emanating from the fuel distribution means can rise in use to create flames extending above the grating, wherein the grating ( 6 ) includes a plurality of grating elements ( 27 ) that together define a walkable working surface for a fire-fighter using the simulator.

[0001] This invention relates to fire-fighter training. In particular,the invention relates to fire-fighter training installations such asthose used to simulate fires in aviation scenarios, notably those ofaircraft crash-landings.

[0002] The invention is not limited to aviation fire-fighting scenarios:it has application in simulators for other fire-fighting scenarios suchas road or railway crashes that, like an aircraft crash-landing, caninvolve a substantial fuel spill. Indeed, preferred aspects of theinvention involve simulators that can be adapted for a variety ofdifferent fire simulations not necessarily involving fuel spillage,including aircraft, collapsed buildings, road-vehicles, trains andmultiple-scenario incidents. Such simulators can also be used for ‘jointservices’ training, i.e. to train members of other emergency services,notably the police and paramedics, who must co-ordinate their work withfire-fighters from time to time.

[0003] Speed and skill are of the essence to all fire-fighters butfire-fighting in aviation scenarios, such as aircraft crash-landings,requires particularly fast response and skilled teamwork if loss of lifeis to be minimised. It is generally accepted that unless a burningcrash-landed aircraft is accessed and the fire suppressed within twominutes of ignition, there is little hope of survival for those on boardwho may have survived the landing itself. As there is so little time formistakes, this places extraordinary demands upon the skill offire-fighters based at civil airports and military airbases. There arecorresponding demands upon the training of those fire-fighters, both asindividuals and as a team, and hence upon the quality of the simulatorson which those fire-fighters practice.

[0004] All substantial airports and airbases have dedicated fire tenderson standby for substantially immediate high-speed access to any crashsite within the airport or airbase perimeter. Such tenders includevehicles known in the art as Major Airport Crashtrucks or MACs. Uponapproaching the stricken aircraft, the practice is to drive the tendersclose to the aircraft for the purpose of laying down fire-retardant foamand simultaneously gaining access to the fuselage of the aircraft tofree its passengers and crew. Indeed, recent practice in civil aviationfire-fighting is to drive a specially-adapted tender right up to theaircraft for the purposes of puncturing its fuselage and injecting foamto protect people who may still be alive within.

[0005] Of course, accidents are characterised by their unpredictabilityand there is no way of knowing what difficulties fire-fighters willencounter when they reach a crash-landed aircraft. Their fire-fightingstrategy must therefore be fully flexible. For example, the orientationof a burning aircraft with respect to the prevailing wind will have aconsiderable influence upon how the fire-fighters can approach theaircraft, suppress the fire and access the fuselage. Also, obstructionssuch as airport vehicles and broken-off engines, undercarriagecomponents, wings or other parts of the aircraft can block access to thefuselage and will, in all likelihood, be on fire themselves. This is allquite apart from the different types of aircraft fire with whichfire-fighters must contend: a fire confined to an engine or theundercarriage, for example, will require a quite different strategy to afire involving spilled fuel.

[0006] The demands of fire-fighter training have led to the emergence offire-fighting simulators in which fluid-fuelled flames are controlled torespond realistically to efforts by trainees to suppress them, inso-called ‘hot-fire’ training. Aviation fire simulators are typicallysited at an airfield or airbase, close to the fire-fighters' base atthat facility. Flame generators can extend across the ground to simulatea fuel spill and can also be associated with mock-ups of above-groundstructures associated with a fire scenario, such as a metal tuberepresenting a section of aircraft fuselage which may have structuresrepresenting wings and engines to one or both sides, or a metal boxrepresenting an airport vehicle. In an analogy apt for acting-outscenarios, these mock-ups are referred to in fire-fighter training as‘props’. That term will be used hereafter in this specification whenreferring to such mock-ups.

[0007] In early days, the fuel used in aviation fire simulators wasliquid fuel such as oil or jet fuel but whilst their flames arerealistic in appearance, those fuels give rise to levels of pollutionthat would be unacceptable today in frequently-used simulators that areoften situated near urban settlements. Consequently, there has been amove toward gas-fuelled simulators and here the challenge is to maintainrealism and controllability.

[0008] The aim of any fire simulator is to mimic the behaviour of aflame as it develops from ignition to eventual extinction. Spilledliquid fuel burns in a similar manner to the same fuel in an open-toppedtank. Upon ignition, the height of the flames is initially quite small.However, the flames progressively grow larger and spread quickly acrossthe full area of the spillage, eventually reaching a limiting heightdetermined by the burning velocity of the flame. The flame grows duringthis phase because its radiant heat promotes the evaporation of liquidfuel. The increased rate of evaporation causes the flame to grow andthis applies additional radiant heat to the remaining liquid fuel,increasing the rate of evaporation still further until the burningvelocity of the flame prevents further flame growth.

[0009] Reference is made at this point to FIG. 1, whose source isDrysdale, D. An Introduction to Fire Dynamics, 2^(nd) edition, p. 12,published in 1998 by John Wiley & Sons. This is a schematicrepresentation of a burning surface showing the heat and mass transferprocesses involved in combustion. Importantly, it shows that in all fireoccurrences, heat flux supplied by the flame (Q_(F)″) transfers to thefuel surface. This heat transfer then increases the volatility of thefuel, hence adding to the conflagration.

[0010] Clearly, therefore, a key aspect of simulating a liquid fuelspill fire is to transmit radiant heat to liquid fuel so as to promotethe evaporation of that liquid fuel.

[0011] An example of a gas-fuelled fire-fighting simulator is disclosedin U.S. Pat. No. 5,055,050 to Symtron Systems, Inc., which comprises adiffuser such as a pan filled with a bed of dispersive medium such aswater or gravel in which a burner system comprising a network ofperforated pipes is submerged or buried. The pipes carry pressurisedliquefied petroleum gas (LPG)—preferably propane—which is initially inits liquid phase but, with reducing pressure, flashes into the vapourphase within the pipes as it approaches the holes in the pipes. Thus,the pipes contain a mix of vaporising liquid propane and propane vapour.The gas issuing from the pipes diffuses as it rises through thedispersive medium and then burns on the surface of the dispersivemedium. Two or more pans can be used side-by-side.

[0012] Whilst such use is not specifically disclosed in U.S. Pat. No.5,055,050, it is well known in the art that the flames can be controlledto respond appropriately to the trainee fire-fighters' actions. Forexample, the fuel flow rate in different parts of the network of pipesor in different pans can be varied under central control via remotevalves. It is also known that the pans can be used beside a prop such asa mock aircraft fuselage to lend further realism to training scenarios.

[0013] The simulator arrangement of U.S. Pat. No. 5,055,050 enjoyscertain benefits such as low cost and is suitable for many trainingrequirements, but the exposed bed of the dispersive medium causesseveral problems that the present invention seeks to overcome.

[0014] One of the major problems of an exposed bed is that thedispersive medium lacks structural integrity and can bear no significantload. This means that props cannot be supported on the bed and thatvehicles cannot drive over the bed without risking fracture of the pipesunderneath the surface and so possibly causing a genuine conflagration.It follows that areas of the simulator are artificially off-limits tofire tenders and, for safety reasons, have to be delineated as such withmarkers or barriers that extend beyond the forbidden area.

[0015] Given the reliance upon close approach of fire tenders toaircraft in aviation fire scenarios, it is hugely unrealistic to preventtenders, in training, accessing areas of the simulator installationthat, in an analogous real fire, correspond to areas around an aircraftupon which the tender would advantageously be driven. This problem isparticularly acute given that tenders must be driven artificially gentlyand slowly during training to avoid accidentally driving onto theforbidden areas: in real life, their drivers will approach an accidentsite at the highest possible speed and brake as hard and late as theycan. It is similarly unrealistic to have to place props beside rather ontop of the bed, where the simulated fire is raging.

[0016] Another disadvantage of the exposed bed of dispersive medium isthat props cannot be dragged across the bed if it is desired torearrange their position: they can only be lifted into place by a crane.This limits the adaptability of the simulator by increasing the cost andtimescale of any changes in the orientation or layout of the props, suchas may be necessary to track changes in wind direction, if indeed suchchanges are possible within the confines imposed by the extent of thebeds surrounding the location of the prop. Aside from developingfire-fighting skills applicable to different situations, the ability tovary training scenarios is important to maintain the trainees' interestand focus.

[0017] There is also the problem that fire-fighter trainees cannot walksafely on the bed of dispersive medium as they fight the simulated fire:even a shallow pan of water is self-evidently unsuitable for access onfoot, and the alternative medium of gravel or other particulaterefractory material presents a trip hazard that could cause a trainee tostumble into the flames. This drawback further deprives the simulator ofrealism, because, in real life, fire-fighters will expect to advance onfoot as they fight back the flames whereas, when using the simulator,their advance will be limited by the margins of the bed.

[0018] Yet another drawback of the exposed bed of dispersive medium isthat the medium can be disturbed by the flow of water used by traineefire-fighters to simulate foam. That flow typically reaches 11,000litres per minute from each nozzle used to fight the fire. Where thedispersive medium is a particulate medium such as gravel, for example,such a powerful jet of liquid can wash the gravel about within the pan,removing gravel from some parts of the pan and piling it up elsewhere inthe pan. At best, this varies the depth of the bed of gravel to thedetriment of optimal dispersion and combustion of the fuel rising fromthe perforated pipes. The behaviour of the simulator may therefore varyunpredictably from one training exercise to the next, unless the gravelis raked back into a level layer between those exercises. At worst,sections of the pipes can be exposed, depriving the out-flowing fuel ofany dispersive effect and exposing the pipes to the full radiant heat ofcombustion.

[0019] The present invention seeks to solve these problems and thereforeto extend the use of gas-fuelled simulators into other parts of thesimulator market, providing a simulator in which the realism of trainingis as great as can be allowed by the safety of those who operate andtrain on it.

[0020] Broadly, the invention resides in a fire simulator comprisingfuel distribution means under a grating through which fuel emanatingfrom the fuel distribution means can rise in use to create flamesextending above the grating, wherein the grating includes a plurality ofgrating elements that together define a walkable working surface for afire-fighter using the simulator. It is further preferred that theworking surface can be driven upon by a fire-fighting vehicle such as afire tender or a Major Airport Crashtruck without damaging the fueldistribution means, and that such a vehicle can drive on and off theworking surface from and onto a surrounding or neighbouring apron. Thesefeatures of the invention enable realistic fire-fighting training bymaking the flames and related scenarios fully accessible tofire-fighters on foot or in a vehicle.

[0021] The aim of the invention is further assisted if the workingsurface is aligned at its periphery with a surrounding or neighbouringapron. To this end, the fuel distribution means is advantageously housedin a recess below the grating, the recess having a base below the levelof the surrounding or neighbouring apron. There may be a pan in therecess containing the fuel distribution means.

[0022] The grating elements may be supported by grating supports thatstand beside the fuel distribution means below the grating elements.Those grating supports can space the grating elements from the fueldistribution means. For easy assembly and reconfiguration, especially insecondary incident training scenarios, the grating elements arepreferably removable from the grating supports and more preferably cansimply be lifted away from the grating supports and out of the workingsurface.

[0023] The grating supports are elegantly defined by a plurality ofhollow support frames, each of which can include upright peripheralwalls surrounding a central cavity. For example, the walls can be in arectangular or square arrangement around a correspondingly-shapedcavity. The walls of the frame lie against the base of the recess or thepan in use and so preferably have lower edge portions shaped to define adrainage opening. Upper edge portions of the frames can be shaped toreceive an array of grating elements that bridge the cavity so that thearray defines a portion of the working surface. For instance, the upperedge portions may be castellated. The support frames are suitably laidin intersecting rectilinear arrays with walls of neighbouring framesaligned with and facing one another. Fixing plates attached to the loweredge of walls of the frame may then provide for fixing the frame to afoundation or base such as the base of the aforementioned recess.

[0024] The support frames are preferably arranged such that a pluralityof grating elements are disposed in a parallel array across the cavity.In that case, where the support frames are laid in a row, theorientations of grating elements in neighbouring frames of that row arepreferably mutually orthogonal. This helps to dissipate the kineticenergy of incoming jets of water and so minimises outwash of anyparticulate material associated with the fuel distribution means underthe grating.

[0025] To accommodate thermal expansion without distortion, it isadvantageous for the grating elements to be movable to a limited extentwith respect to the support frame. Elegantly, movement of the gratingelements can be limited by encountering a neighbouring support frame.

[0026] The invention can be applied to various burner arrangementsincluding those in which the fuel distribution means is buried,submerged or exposed. Thus, for example, the fuel distribution means maybe covered by a fuel-dispersive medium from which dispersed fuel risesthrough the grating. In that case, the fuel-dispersive medium can beaccommodated in the cavities of an array of support frames to define abed extending under the working surface that is subdivided by the wallsof those support frames.

[0027] It is also possible for the fuel distribution means is associatedwith fuel-heating means for applying to the fuel distribution meansradiant heat that emanates from the flames in use, thereby promotingvaporisation of liquid fuel in the fuel distribution means. Thefuel-heating means can absorb radiant heat emanating from the flames andthen radiate to the fuel distribution means some of the heat thusabsorbed. The fuel-heating means can also reflect some of the radiantheat emanating from the flames.

[0028] The simulator of the invention can further include a servicetrench being surrounded by or bordering the working surface thatincludes a movable or removable access cover lying flush with theworking surface. That cover can be vented to permit free venting ofgases from the service trench and where the service trench containscontrol equipment for lighting and fuelling the flame, the trenchpreferably defines walls having cavities into which the controlequipment is recessed for protection from heat and water. The servicetrench can also drain fire-fighting water or rainwater that runs throughthe grating.

[0029] It is greatly preferred if the grating elements remain below 200Celsius in use, as this is the usually threshold for the use of standardfire-fighter personal protection equipment such as footwear.

[0030] The simulator of the invention enables a prop to be supported byits working surface, and for the prop to be moved across the workingsurface while being supported by the working surface.

[0031] This International patent application claims priority from theApplicant's United Kingdom Patent Application Nos. 0005012.0, 0014311.5and 0102569.1, the contents of which are incorporated herein byreference. Those applications are not continuing in their own right asthey refer to prototype development but copies of them are available onthe public file of this application, from the date on which thisapplication is published. The discussion of flame characteristics andtheir testing and analysis set out particularly in Application Nos.0005012.0 and 0014311.5 may be of background interest to readers of thisspecification.

[0032] In order that this invention may be more readily understood,reference will now be made, by way of example, to the accompanyingdrawings in which:

[0033]FIG. 1, which has already been described, is a diagram of aburning surface;

[0034]FIG. 2 is a schematic sectional side view of a fuel spillsimulator in accordance with a first embodiment of the invention;

[0035]FIG. 3 is a perspective view of a serpentine array of fueldistribution pipes being part of the first embodiment of the invention;

[0036]FIG. 4 is a schematic sectional side view of a fuel spillsimulator in accordance with a second embodiment of the invention;

[0037]FIG. 5 is a schematic sectional side view of a fuel spillsimulator in accordance with a third embodiment of the invention;

[0038]FIG. 6 is a perspective view of an array of support frames laidover serpentine arrays of fuel distribution pipes, as part of the thirdembodiment of the invention;

[0039]FIG. 7 is a perspective view corresponding to FIG. 6 but showinggravel laid over the fuel distribution pipes within all of the supportframes and grating bars laid on some of those support frames over thegravel;

[0040]FIG. 8 is an enlarged perspective view of one of the supportframes of FIG. 7, with the grating bars partially cut away to showgravel within the frame and that gravel being partially removed to showa fuel distribution pipe normally buried by the gravel;

[0041]FIG. 9 is a perspective part-sectioned view of part of the arrayof support frames bordering the central trench of FIG. 5, showing theirdrainage provisions;

[0042]FIG. 10 is a schematic perspective view of a substantiallycomplete simulator corresponding to FIG. 5;

[0043] FIGS. 11(a) and 11(b) are schematic plan views of a simulatorcorresponding to that shown in FIGS. 5 and 10, showing how a prop suchas a mock-up aircraft can be positioned and re-positioned on the workingsurface;

[0044]FIG. 12 is a partial schematic perspective view of a simulatorarrangement suitable for Secondary Incident Training (SIT) scenarios;

[0045]FIG. 13 is a partial schematic perspective view of the simulatorarrangement of FIG. 12, but showing a SIT prop on the working surface ofthe simulator and enabled for use; and

[0046]FIG. 14 is a schematic plan view of a simulator having a main propand showing locations for siting auxiliary SIT props used to enactvarious SIT scenarios.

[0047] Referring firstly to FIG. 2 of the drawings, in a firstembodiment of the invention, a fuel spill simulator 1 comprises a steelpan 2 set into concrete foundations 3 that support the pan 2. The pan 2may, for example, be circular or rectangular in plan, and is bordered byservice trenches 4 that contain control equipment 5 and services such asfuel supply pipework and power or control cabling (not shown). Thetrenches 4 shown in FIG. 2 may, of course, represent opposed sections ofone continuous trench 4 that surrounds the pan 2.

[0048] The pan 2 and the trenches 4 are surmounted by a grating 6 thatdefines a flat, level working surface on which a trainee fire-fightercan walk and upon which a fire-fighting vehicle can preferably drive.Full details of the grating 6 will be given later. In the embodimentillustrated, the working surface defined by the grating 6 extends beyondthe trenches 4 into neighbouring or surrounding areas 7 on the otherside of the trenches 4 from the pan 2, which areas may surmountneighbouring pans of similar design. In any event, the grating 6 shouldbe flush with the neighbouring or surrounding areas 7 to minimise triphazards and will eventually extend to a contiguous concrete apron orblockwork surface (not shown) with which it preferably defines acontinuous substantially level surface.

[0049] The base of the pan 2 is dished slightly to promote drainage offire-fighting water W or precipitation through a central drain 8, fromwhich the water W is preferably filtered and recycled. The pan 2supports a layer of gravel 9 of substantially uniform thickness and aplurality of vertical grating supports 10 that support the grating 6 atintervals across its width over the pan 2. The supports 10 extend fromthe grating 6 to the pan 2 and so extend through a mesh 11 over thegravel 9 such that their base portions are surrounded by gravel 9. Itwill be evident that in view of the dished shape of the pan 2, thesupports 10 are of various lengths to suit their position with respectto the centre of the pan 2, while keeping the grating 6 level.

[0050] Exposed fuel distribution pipework 12 constituting a burnerextends over the gravel layer 9 and the mesh 11 and around the supports10 in a sinuous, serpentine array. The pipes 12 of the array arepreferably of maintenance-free stainless steel. As can be seen in FIG. 3which shows an array of pipes 12 over the pan 2 but omits theintermediate gravel layer 9 for clarity, the pipes 12 are perforated todefine downwardly-facing orifices, holes or nozzles for the egress ofpropane supplied from a supply pipe 13 leading from control equipment 5within the trench 4 beyond the outer edge of the pan 2. The propane isin the liquid phase under pressure before it enters the pipes 12, butflashes into the vapour phase as it flows through the pipes 12 beforeits emergence from the orifices, holes or nozzles in the pipes 12,whereupon the gas streams downwardly to approach the gravel layer 9.

[0051] During its journey through the pipes 12, a mix of propane vapourand swiftly-vaporising liquid propane is warmed by the radiant heat towhich the pipes 12 are exposed. This promotes the evaporation of theremaining liquid fraction and the flammability of the fuel as a whole,which beneficially simulates the behaviour of a real fuel spill. Theradiant heat radiates downwardly from the flames above the grating 6 andupwardly from the gravel layer 9, this latter radiation being due toreflection of radiant heat that originated from the flames, and heatingof the gravel layer 9 itself by that heat. The openings of the grating 6are large enough to permit substantial radiant heat flux to pass throughthe grating 6, but not so large as to present a trip hazard forfire-fighters walking on the working surface defined by the grating 6.

[0052] As can be seen in the enlarged detail view included in FIG. 2, anarray of parallel or intersecting rods 14 sandwiched between the gravel9 and the pan 2 act as groynes to resist movement of the gravel 9 withrespect to the pan 2, especially down the slope of the dished pan base.Where the rods 14 intersect, they are preferably interlaced in wovenmanner to define openings for water drainage down the dished shape ofthe pan base 2. Retention of gravel 9 is further assured by theaforementioned wire mesh 11 that lies on top of the layer of gravel 9under the fuel distribution pipework 12. Once heated in use, that mesh11 can further contribute to the upwardly-radiating heat that warms thefuel distribution pipes 12 and the propane streams emanating from thosepipes 12.

[0053] The enlarged detail view included in FIG. 2 also makes plain thatthe gravel 9 comprises various particle sizes. To be specific, the stonespecification is of igneous rocks selected from the following group ofclassifications, namely: fine-grained granite; diabase; gabbro; basalt;and rhyolite. The stone is crushed and provided as sized aggregateconforming to ASTM-C33, grade 2 (or equivalent), as follows: Sieve Size(nm) 100% 75 90-100% 65 35-70% 50  0-15% 40  0-5% 20

[0054] As can be seen in FIGS. 2 and 3, each trench 4 beside the pan 2contains a fuel supply control unit for regulating the supply of fuel tothe fuel distribution pipes 12 and a pilot control unit for lighting thefuel ejected from the pipes 12, which units are shown together ascontrol equipment 5 hung on a side wall of the trench 4. The trench 4 isclosed in use by a porous lid 15 under the grating 6 (omitted from FIG.3), which lid serves to protect the control equipment 5 from radiantheat but can be opened to afford access to the control equipment 5 whenrequired. The trench 4 also contains an air pipe 16 whose purpose is topurge the trench 4 of flammable and potentially explosive gases that maybuild up in use, when the trench 4 is closed by the lid 15. The air pipe16 does this by introducing air to pressurise the trench 4: this helpsto prevent dangerous contaminants entering the trench 4 and forcesexcess air together with any contaminants out of the trench 4 throughthe porous lid 15.

[0055] The embodiment of FIG. 4 is broadly analogous to that of FIGS. 2and 3 in that it provides for full vaporisation of fuel by downwardprojection above gravel 9, so like numerals are used for like parts. Thekey differences are that, in FIG. 4:

[0056] the pan 2 is cambered so that water runs outwardly from thecentre and drains into the trench(es) 4;

[0057] the supply pipes 13 that supply the fuel distribution pipework 12are centrally located with respect to the pan 2, inboard of the fueldistribution pipework 12, rather than being at the outer edge of the pan2;

[0058] the trenches 4 lack lids and so are open in the sense that theyvent freely to atmosphere through vented covers 17; and

[0059] the control equipment 5 is recessed into cavities in the trenchwall for protection from heat and water.

[0060] The relative simplicity of the FIG. 4 embodiment will be evidentupon comparing the drawings, which reduces its cost in comparison withthe FIG. 2 embodiment but without sacrificing performance. Specifically,the trenches 4 perform the dual function of housing and providing accessto the control equipment 5 and also draining water from the pan 2. Thisobviates the central dedicated drain 8 of FIG. 2. Furthermore, the opentrench design provides inherent explosion relief without the need forthe purging air pipes 16 of FIG. 2. Being recessed into the trench wall,the control equipment 5 no longer needs the protection of the porous lid15 from radiant heat, but it will need to be positioned above themaximum water level that is predicted to be in the trench 4 under themaximum flow rate of incoming water W in use. It will also be apparentthat the inboard supply pipes 13 that supply the fuel distributionpipework 12 can be shorter and simpler than the outboard supply pipes 13of FIG. 2.

[0061] The embodiment of FIG. 5 also shares some features with theembodiments of FIGS. 2 and 4 and so again, like numerals are used forlike parts. Unlike the embodiments of FIGS. 2 and 4, there is no pan;instead, a steel-edged recess is simply formed in a concrete slabfoundation 3 to contain a layer of gravel 9. A typical depth for thisrecess would be up to 500 mm but this depends on the drainagerequirements and what the total finished area of the simulator might be.

[0062] The gravel 9 is surmounted by a grating 6, preferably lying flushwith the surrounding concrete or blockwork apron 18, that stands onvertical supports 10 extending upwardly from the base of the recess. Inthis embodiment, a trench 4 extends centrally along the recess and, asshown in the enlarged detail view included in FIG. 5, the fueldistribution pipework 12 lies on the base of the recess and so isdisposed below the gravel layer 9. Again, the pipework 12 is perforatedto define a series of holes, apertures or nozzles to eject fuel in use,but unlike the embodiments of FIGS. 2 and 4 which eject fuel downwardlyfor maximum evaporative effect, the fuel of the FIG. 5 embodiment can beejected in any direction as it is intended to be dispersed by the gravel9 in any event.

[0063] As in FIG. 4, the trench 4 of the FIG. 5 embodiment is closed bya vented cover 17 so as to vent explosive gases to atmosphere and thecontrol equipment 5 is recessed into cavities in the trench walls. Also,whilst no camber or dish is evident from FIG. 5, the base of the recessis very gently inclined, sloped or dished toward the trench 4 to promotedrainage of water from the gravel layer 9. It is advantageous that waterdoes not drain away too quickly, so as to allow enough time for theflare-off of unburned gas; otherwise, that unburned gas may be entrainedin a fast-moving stream of water and swept away to cause dangerous gasaccumulations downstream.

[0064] To describe the grating 6 and its supports 10 in detail, thedescription of the FIG. 5 embodiment will now continue with reference tothe remaining drawings. It will be evident to the skilled reader how thegrating 6 and supports 10 shown in those drawings can be adapted to suitthe embodiments of FIGS. 2 and 4 in which, unlike FIG. 5, the fueldistribution pipework 12 is exposed above the gravel layer 9. Inparticular, it will be readily apparent how most if not all of thegrating features of the FIG. 5 embodiment can be applied to thepreceding embodiments if a suitably adapted support is used.

[0065] Referring then to FIGS. 6 to 9 of the drawings, theabovementioned grating supports 10 are defined by the upstanding walls10A, 10B of fabricated square support frames 20 that are open to theirtop and bottom and that lie upon and are fixed to the base of the recessof FIG. 5. As best shown in FIGS. 6 and 7, the support frames 20 fittogether in rectilinear arrays in mutually-abutting modular fashion, sothat each support frame 20 helps to support its neighbours against sideloadings in use. The walls 10A, 10B of the various support frames 20thus lie in orthogonally-intersecting vertical planes.

[0066] Looking at any one of the support frames 20 as shown in FIG. 8,it will be noted that each of its four walls 10A, 10B is a flat elongateplate that is preferably of mild steel. Each plate is welded at each ofits opposed ends to a respective orthogonally-disposed neighbouringplate, the welded junctions between the plates thus defining the cornersof the square between the walls. Additionally, each plate has a cut-out21 extending along one of its long edges, namely the lower edge that isdisposed generally horizontally and facing downwardly in use. The endsof the cut-outs 21 are defined by feet 22 that have a square fixingplate 23 welded to them at the lower corners of the support frame 20.Each fixing plate 23 is therefore arranged to lie flat against the baseof the recess and it is pierced by a through-hole (not shown) thatenables the support frame to be bolted or otherwise fixed to the base.Whilst not essential, it is preferred that the support frames 20 arefixed down in this way so as to prevent excessive sideways movement or‘shuffling’ of the support frames as vehicles drive over the workingsurface of the simulator.

[0067] The cut-outs 21 in the walls of the support frames 20 align withthose of neighbouring support frames 20 in use, and have the dualfunction of accommodating the serpentine arrays of fuel distributionpipes 12 previously fixed at appropriate locations to the base of therecess, and of permitting water W to drain across the base of the recesstoward the central trench of FIG. 5. Specific reference is made to FIG.9 in this respect.

[0068] The plates defining two opposed walls 10B of each support frameare further provided with castellated upper edges defined by a row ofupstanding oblong teeth 24 alternating with, and delineated by, oblongslots 25. As will be most apparent from FIGS. 7 and 8, the purpose ofthe castellations is to hold a set of oblong-section steel grating bars26 bridging the open top of the support frame 20 in a parallel spacedarray that defines a substantially flat, if locally slightly inclined,working surface level with the upper edges of the walls 10A, 10B and theteeth 24. Thus, the castellations hold the grating bars 26 at a suitableheight above the fuel distribution pipes 12, and keep those bars 26 inthe correct position during use of the simulator.

[0069] To this end, each grating bar 26 is held at one end in a slot 25of one castellated wall 10B and at the other end by the correspondingslot 25 of the opposite castellated wall 10B. It will also be apparentfrom the drawings that the major cross-sectional axis of each gratingbar 26 is oriented vertically to maximise its load-bearing abilityagainst loads moving over the grating 6.

[0070] In practice, the grating bars 26 are fitted into the slots 25only after the aforementioned layer of gravel 9 in the form of igneousstone chippings or other particulate dispersive medium has been pouredinto the open support frames 20 around the fuel distribution pipes 12,burying them to a depth of say 120 mm. The layer of gravel 9substantially fills the space around the fuel distribution pipes 12between the grating bars 26 and the base of the recess. It will beapparent that the gravel 9 has little room to move when so positionedand that any tendency it might have to shift sideways across the recessis limited by the baffle effect of the walls 10A, 10B that effectivelypartition the gravel bed 9.

[0071] It will also be noted, with particular reference to FIGS. 6, 7and 10, that neighbouring support frames 20 in rows or columns of thearray within the recess are turned through 90° with respect to eachother so that their castellated walls 10B never abut one another. Thus,as best shown in FIG. 10, the grating bars 26 define cells 27 in rows orcolumns corresponding to the support frames 20 and the grating bars 26of adjacent cells are mutually orthogonal. This alternating arrangementcan be appreciated in the check pattern extending over the workingsurface of the simulator.

[0072] The functional significance of the alternating arrangement of thegrating bars 26 is twofold. Firstly, the grating bars 26 are free toslide longitudinally within their slots 25 for the purposes of thermalexpansion without distortion but once they have slid to a limited extent(a maximum of 10 mm in the preferred embodiment), they will bear againstthe non-castellated wall 10A of a neighbouring support frame 20 and socan slide no further. This is important under the dynamic sideways loadslikely to be imparted by a swerving or braking fire tender or otheremergency vehicle. Secondly, a major benefit of the grating 6 is itsability to dissipate the flow of incoming jets of water or otherfire-fighting agents and so to prevent the dispersive medium beingdisturbed by those jets being played directly on the working surface ofthe simulator. As the dissipating effect of a straight grating of whollyaligned elements might conceivably be overcome if the incoming jet isaligned with the elements, the alternating arrangement of grating bars26 has the benefit that it will reliably disrupt jets of water strikingthe working surface from any angle. In any event, any water that doesget through the working surface while retaining damaging momentum willbe dissipated by the baffle effect of the walls 10A, 10B between thesupport frames 20, under the working surface.

[0073] To help visualise the size of each frame 20, and strictly by wayof example only, their pitch or spacing between centres is nominally 1metre and so the overall width of each frame is 990 mm square to leave athermal expansion gap of 10 mm all round. The walls 10A, 10B of eachframe are 25 mm thick and stand a total of 200 mm above the base of therecess. Each grating bar 26 is of 80 mm×30 mm black bar and the slots 25that receive the grating bars 26 are of corresponding dimensions. About170 mm is therefore available under the grating bars 26 and above thebase of the recess to accommodate the fuel distribution pipes 12 and thesurrounding layer of gravel 9. The spacing between neighbouring gratingbars 26 of a given support frame 20 is no greater than 33 mm so as topresent no trip hazard to trainee fire-fighters walking on the workingsurface. The pitch or spacing between centres of the grating bars 26 istherefore nominally 66 mm and there is provision for thirteen of suchbars 26 on each support frame 20.

[0074] A grating specified as above can withstand the maximum wheel loadof a Major Airport Crashtruck (MAC). Performing structural analysisaccording to the requirements of BS5950:Part1:1985 using ANSYS 5.0A, andassuming a mass of the tender of 501.1 kN and a maximum axle load of 130kN, the grating can comfortably withstand braking from 20 kph.

[0075] Moreover, the considerable mass of the grating bars 26 (in theorder of 250 kg/m²) imparts thermal inertia that makes them slow toattain damaging temperatures. During typically short bursts of use fromcold (anything longer than three minutes of practice fire-fighting israre in view of the need for extreme speed in real-life aviationfire-fighting), their temperature keeps well within the parametersappropriate to ordinary personal protection equipment (PPE) routinelyworn by fire-fighters. Fire-fighter protective footwear and other PPE israted to withstand temperatures up to 200 Celsius; tests show that themass of the grating bars 26 keeps their temperature to about 180 Celsiuseven after exposure to the radiated heat flux of a fire with flametemperatures between 700 and 1100 Celsius.

[0076] A beneficial side-effect of the considerable girth of the gratingbars 26 is that corrosion will not significantly reduce theircross-section and hence load-bearing strength during their projectedworking life. Consequently, the working surface of the simulator needsno expensive or fragile corrosion treatments, and is essentiallymaintenance-free.

[0077] The load-bearing ability of the working surface is heightened bythe elegant design of the fabricated support frames 20, in whichdownward loads are transferred directly to the foundations through thevertical walls 10A, 10B without putting the aforementioned welds underdamaging tensile or bending loads.

[0078] As already mentioned, the embodiment shown in FIG. 5 et seq ismodular in nature. Specifically, it is envisaged that a standard modulecomprises a serpentine fuel distribution pipe 12, an associated fuelsupply control unit and nine support frames 20 in a 3×3 array and hence,with the above dimensions, gives a working surface that covers 9 m².Several such modules can be used together to construct a simulatorhaving a working surface of any required size, such as the one shown inFIG. 10 which comprises eight modules on each side of the central trench4, giving a total working area of 144 m² excluding the area of thetrench 4 itself. In practice, the working area of a simulator willgenerally be substantially greater so that large props can be placed onthe working surface and correspondingly wide-ranging fuel spills can besimulated.

[0079] The central trench 4 featured in FIGS. 5, 9 and 10 is covered bya removable vented cover 17 as shown in FIGS. 5 and 10, which can belifted when it is necessary to gain access to the control equipment 5and ancillary equipment, such as valve trains and service pipework,within the trench 4.

[0080] FIGS. 11(a) and 11(b) show how a prop 28, in this case a mock-upof a military jet, can be placed freely on the working surface of asimulator akin to that of FIG. 10. In both drawings, the prop 28 isaligned with the prevailing wind shown by the arrows as this is thedirection in which a crash-landed aircraft is most likely to lie,although other angles to the prevailing wind can obviously be simulatedfor wide-ranging practice. In FIG. 11(a), the prevailing wind is offsetby about 30° with respect to the central trench 4 of the simulator andthe central longitudinal axis of the prop 28 is similarly aligned.However in FIG. 11(b), the prevailing wind is aligned with the trench 4and the prop 28 has been re-aligned accordingly and also advanced acrossthe working surface. Highly advantageously, the prop 28 can simply bedragged across the working surface from one orientation to the other,with no need of a crane to lift the prop 28.

[0081] Moving on finally to FIGS. 12, 13 and 14, these drawingsillustrate a further embodiment of the invention suitable forfire-fighter training involving so-called secondary incidents.Specifically, a main or primary incident—for example, an aircraft crashlanding—could well be accompanied by one or more secondary incidentssuch as a collapsed building hit by the aircraft or a burning airportvehicle set alight by a fuel spill from the aircraft. Training for thatkind of eventuality is known in the art by the acronym SIT, standing forSecondary Incident Training.

[0082] The embodiment of FIGS. 12, 13 and 14 caters for SIT by providingone or more locations on and under the working surface of the simulatorthat can be adapted to enable the use of one or more secondary props inparallel with, or instead of, a main prop. This is achieved by theprovision of a channel 30 formed in the base 31 of the recess, whichchannel 30 extends from the central trench 4 under the fuel distributionpipes 12 to a desired location under the working surface. The channel 30itself is best shown in FIG. 12, whereas FIG. 13 shows the channel 30filled with service supply links 32 (such as a pilot fuel duct, a mainflame fuel duct and control/electronics cabling) and terminating in aSIT control unit 33 to which those service supply links 32 run. In thisway, each channel 30 contains the services necessary to fuel and controla small SIT scenario.

[0083] In normal use of the simulator with a main prop (not shown), theservice supply links 32 and the SIT control unit 33 remain dormant underthe grating 6, which continues to present an uninterrupted workingsurface. Indeed, the fuel distribution pipes 12 remain undisturbed andso, with suitable heat-shielding, the service supply links 32 and theSIT control unit 33 can be left buried under gravel 9 for the purposesof normal fire simulation, burning fuel supplied via the fueldistribution pipes 12 at that location.

[0084] When a SIT scenario is to be enacted, a small SIT prop 34 (inthis case, resembling a car that will simulate a small vapour fire) isdragged across the working surface to near the location of the SITcontrol unit 33. The service supply links 32 and the SIT control unit 33can then be enabled simply by removing sufficient grating bars 26 (whichlift out easily from their castellated support frames 20) and underlyinggravel 9 to gain access to the SIT control unit 33, whereupon theflexible connections 35 necessary to bring pilot fuel, main fuel,control signals and electrical power to the nearby SIT prop 34 cansimply be plugged into the SIT control unit 33. The flexible connections35 can be shrouded by a protective sleeve (not shown) if they areexposed to flame, as they will be in FIG. 13, although some SIT propsmay make provision for internal connection to the SIT control unit 33 insuch a way that the prop itself shields the connections from the flames.

[0085] Only one channel 30 is illustrated in FIGS. 12 and 13 for thepurposes of clarity. However, for optimum flexibility, there arepreferably a few similarly-equipped channels 30, such as four of them,leading to different locations dispersed around the working surface ofthe simulator. Such an arrangement is shown in FIG. 14 in which a mainprop 36 representing a full-size Boeing 747-400 aircraft, which isoptionally a permanent fixture, has extensive fuel spill simulators 37to the port and starboard sides. Here, four locations for possible SITscenarios are represented as blocks 38. One example could be a SIT propfabricated to represent a re-fuelling tanker servicing the aircraft andso located near a wing 39, and a multi-scenario training exercise couldbegin with an incident with the tanker, escalating to a fuel spill fire,escalating to a larger fuel spill fire and finally involving theaircraft itself. The simulated fire could spread to, or the scenariocould otherwise involve, other SIT props at other locations on theworking surface of the simulator.

[0086] In general, the props can be moved, swapped and interchanged withgreat flexibility to create fresh training scenarios involvinginteraction between a main incident, a fuel spill and one or moresecondary incidents, that can be adapted readily to suit the prevailingweather and the needs of the trainees. This fosters the ability to setup ‘joint services’ training involving combinations of fire, police andparamedic services, and ensures that scenarios remain instantlycontrollable so that if, for example, a genuine incident occurs duringtraining, crews can break off from training and attend that incidentwithout delay.

[0087] Many variations are possible within the inventive concept. Forexample, whilst a gravel bed is preferred as a dispersive medium wheresuch a medium is to be used, the grating of the invention couldalternatively be used over a pan of water acting as the dispersivemedium. Consequently, reference should be made to the appended claimsand to other conceptual statements herein rather than to the foregoingspecific description in determining the scope of the invention.

1. A fire simulator comprising fuel distribution means under a gratingthrough which fuel emanating from the fuel distribution means can risein use to create flames extending above the grating, wherein the gratingincludes a plurality of grating elements that together define a walkableworking surface for a fire-fighter using the simulator.
 2. The simulatorof claim 1, wherein the working surface can be driven upon by afire-fighting vehicle such as a fire tender or a Major AirportCrashtruck without damaging the fuel distribution means, which vehiclecan drive on and off the working surface from and onto a surrounding orneighbouring apron.
 3. The simulator of claim 1 or claim 2, wherein theworking surface is aligned at its periphery with a surrounding orneighbouring apron.
 4. The simulator of claim 2 or claim 3, wherein thefuel distribution means is housed in a recess below the grating, therecess having a base below the level of the surrounding or neighbouringapron.
 5. The simulator of claim 4, wherein a pan in the recess containsthe fuel distribution means.
 6. The simulator of any preceding claim,wherein the grating elements are supported by grating supports thatstand beside the fuel distribution means below the grating elements. 7.The simulator of claim 6, wherein the grating elements are removablefrom the grating supports.
 8. The simulator of claim 7, wherein gratingelements can be lifted away from the grating supports and out of theworking surface.
 9. The simulator of any of claims 6 to 8, wherein thegrating elements are spaced from the fuel distribution means by thegrating supports.
 10. The simulator of any of claims 6 to 9, wherein thegrating supports are defined by a plurality of hollow support frames.11. The simulator of claim 10, wherein each support frame includesupright peripheral walls surrounding a cavity.
 12. The simulator ofclaim 11, wherein walls of the frame have lower edge portions shaped todefine a drainage opening.
 13. The simulator of claim 11 or claim 12,wherein walls of the frame have upper edge portions shaped to receive anarray of grating elements that bridge the cavity, the array defining aportion of the working surface.
 14. The simulator of claim 13, whereinthe upper edge portions are castellated.
 15. The simulator of any ofclaims 11 to 14, wherein the walls are in a rectangular or squarearrangement around a correspondingly-shaped cavity.
 16. The simulator ofclaim 15, wherein the support frames are laid in intersectingrectilinear arrays with walls of neighbouring frames aligned with andfacing one another.
 17. The simulator of any of claims 11 to 16, whereina plurality of grating elements are disposed in a parallel array acrossthe cavity.
 18. The simulator of claim 17, wherein the support framesare laid in a row and wherein the orientations of grating elements inneighbouring frames are mutually orthogonal.
 19. The simulator of any ofclaims 11 to 18, wherein fixing plates attached to the lower edge ofwalls of the frame provide for fixing the frame to a foundation or base.20. The simulator of any of claims 11 to 19, wherein the gratingelements are movable to a limited extent with respect to the supportframe.
 21. The simulator of claim 20, wherein movement of the gratingelements is limited when the grating elements encounter a neighbouringsupport frame.
 22. The simulator of any preceding claim, wherein thegrating elements are elongate bars each having at least one face thatdefines part of the working surface when the bar is oriented generallyhorizontally for use.
 23. The simulator of any preceding claim, whereinthe fuel distribution means is covered by a fuel-dispersive medium fromwhich dispersed fuel rises through the grating.
 24. The simulator ofclaim 23 when appendant to claim 11, wherein the fuel-dispersive mediumis accommodated in the cavity and defines a bed extending under theworking surface subdivided by the walls of a plurality of supportframes.
 25. The simulator of any of claims 1 to 22, wherein the fueldistribution means is associated with fuel-heating means for applying tothe fuel distribution means radiant heat that emanates from the flamesin use, thereby promoting vaporisation of liquid fuel in the fueldistribution means.
 26. The simulator of claim 25, wherein thefuel-heating means absorbs radiant heat emanating from the flames andradiates to the fuel distribution means some of the heat thus absorbed.27. The simulator of claim 25 or claim 26, wherein the fuel-heatingmeans reflects some of the radiant heat emanating from the flames. 28.The simulator of any of claims 25 o 27 wherein the fuel-heating meansincludes a layer of particulate refractory material.
 29. The simulatorof claim 28, wherein a foraminous sheet or mesh is interposed betweenthe fuel distribution means and the layer of particulate refractorymaterial.
 30. The simulator of any preceding claim, further including aservice trench being surrounded by or bordering the working surface andincluding a movable or removable access cover that lies flush with theworking surface.
 31. The simulator of claim 30, wherein the cover isvented to permit free venting of gases from the service trench.
 32. Thesimulator of claim 30 or claim 31, wherein the service trench containscontrol equipment for lighting and fuelling the flame, and defines wallshaving cavities into which the control equipment is recessed.
 33. Thesimulator of any of claims 30 to 32, wherein the service trench drainsfire-fighting water or rainwater that runs through the grating.
 34. Thesimulator of any preceding claim and being arranged such that thegrating elements remain below 200 Celsius in use.
 35. The simulator ofany preceding claim and including a prop supported by its workingsurface.
 36. The simulator of claim 35, wherein the prop can be movedacross the working surface while being supported by the working surface.37. A fire simulator, substantially as hereinbefore described withreference to or as illustrated in FIGS. 2 and 3, FIG. 4 or FIGS. 5 to 14of the accompanying drawings.